Each of the original Chaos Theory releases (PS2, Xbox, GC, Windows) were available in a limited edition. However every indication I can find is that the Gamecube version's packaging was mislabeled and doesn't include the additional disc. There isn't space in the box either, the game is already two discs on GC.
Anyone know for certain whether a Gamecube compatible bonus disc was produced, and how it was distributed? Places like Wikipedia say you could contact Ubisoft, but I doubt they'd provide one now.